Hydrogen passivation and reactivation of the Al-acceptors in p-type 6H-SiC

Abstract

We report on the passivation by hydrogen and the subsequent thermal reactivation of the acceptors in Al-doped p-type 6H-SiC. Capacitance-voltage measurements revealed that the near-surface free carrier concentration was reduced by at least an order of magnitude after hydrogen plasma treatment. The thermal stability of the Al-H complex in hydrogenated SiC was investigated through a series of isothermal anneals at temperatures ranging from 200 to 275 °C, while applying a reverse bias to a Ru Schottky barrier. Ru was chosen as the Schottky barrier metal for both its permeability to hydrogen as well as its thermal stability. The electric field associated with the applied reverse bias caused the dissociated hydrogen to drift deeper into the material, thereby confirming the positive charge state of atomic H in p-type SiC. The thermal dissociation of the electrically neutral Al-H complex was found to obey first-order kinetics for temperatures above 225 °C with a dissociation energy of (1.51±0.12) eV.

Diffusion of hydrogen in perfect,p-type doped, and radiation-damaged4H−SiC

“…Therefore, the limiting process in the diffusion becomes the trapping and detrapping of hydrogen into/from B + H or Al+ H complexes. Our estimate for the dissociation energy, 2.5 and 1.6 eV, respectively, are in (possibly fortuitously good) agreement with the experimentally observed reactivation energies of the acceptors, 2.5 and 1.6 eV, 8,12 and also with the effective diffusion activation energies measured in Ref. 11.…”

Single versus double ion implantation: a deep level study

“…Heat treatments up to 1000 °C (no bias applied) resulted in a gradual and partial reactivation of dopants in the region close to the surface (0.4 < x < 0.8 µm) similarly to what has been reported by Samiji et al [12], while Achtziger et al [11] obtained reactivation of dopants after annealing at temperatures as low as 250 °C under reverse bias conditions. After annealing at 1500 °C, the value of N A is restored close to the initial as-grown conditions and a slight increment is also observed.…”

Point Defects in Silicon Carbide

“…The positively charged H is experimentally confirmed in p-type SiC Samiji et al, 2001). Figure 14 shows the net hole concentration profiles of a deuterium ( 2 H)-passivated Al-doped p-type SiC Schottky barrier diode (SBD) recorded as a function of time after the deuterium treatment .…”

“…The incorporated H concentration is significantly lower than the acceptor doping concentration (1 Â 10 18 cm À3 ), and the net hole concentration did not change after the H 2 annealing. In this context, it can be mentioned that the Al-H complex starts to dissociate at much lower temperature ($300°C) ( Janson et al, 2001;Samiji et al, 2001) than 1000°C, and acceptor passivation by H cannot be a reason for the carrier lifetime improvement. Hence, there seem to be deep-level defects which act as carrier lifetime killers in p-type layers, similar to that in n-type layers.…”